Fix: Created default decorator - user doesn’t have to declare

Author: danvick

lib/src/inputs/form_builder_date_time_picker.dart

@@ -24,7 +24,7 @@ class FormBuilderDateTimePicker extends StatefulWidget {
     this.format,
     this.firstDate,
     this.lastDate,
-    this.decoration,
+    this.decoration = const InputDecoration(),
   });
 
   @override

lib/src/inputs/form_builder_slider.dart

@@ -20,7 +20,7 @@ class FormBuilderSlider extends StatefulWidget {
     @required this.initialValue,
     this.validators = const [],
     this.readonly = false,
-    this.decoration,
+    this.decoration = const InputDecoration(),
     this.divisions,
   });